The present invention relates to a new circuit design which permits precision triggering of a load during predetermined phases of an A/C cycle and to control the activation of a load. In prior art applications, a triac or thyristor is often used to perform phase control of the A/C cycle. In one common application involving outdoor electric lights, phase control of the A/C cycle is used to dim the light source. A drawback in using a triac or thyristor, however, is that the device will only deactivate at zero crossing in the A/C cycle. Thus, to phase control a load with a triac or thyristor, it must be triggered sometime after zero crossing which will lead to an increase in electromagnetic interference (EMI) and the ability to deactivate a load when desired.
The present invention solves the above mentioned design problems by providing circuitry which uses a high side mosfet drive that may be activated and deactivated at any point in the A/C cycle. To do this, the circuitry of the present invention uses an A/C line to activate the mosfet drive and to charge a capacitor during the positive phase of the A/C cycle. During the negative phase, the circuitry is designed to use the discharge of the capacitor to activate the mosfet drive, if desired.